Over the past several years, endodontic instruments such as root canal files have been manufactured by simultaneously grinding and twisting thin carbon steel or stainless steel rods or wires. Specifically, steel wire blanks are first ground to the desired cross sectional shape, such as square, triangular or rhomboid, and to the appropriate size and taper. The ground blank is then gripped at one end and spring loaded jaws are brought into contact with the ground portion of the blank. As the blank is rotated from the gripped end, the jaws are moved axially away from that end. The jaws therefore twist the rotating blank and form helical flutes into the blank. The longitudinal, ground edges of the blank form helical cutting edges on the file. The axial jaw speed, twisting speed and spring force are controlled to obtain the desired helical configuration.
With the emergence of superelastic materials, such as nickel titanium alloys, endodontic instrument manufacturers are now able to form endodontic root canal files with much more flexibility. This greatly assists the endodontist during use of the file in a root canal procedure. The use of superelastic material, however, causes some significant manufacturing concerns due to the tendency of the material to return to its original shape after the release of an applied force. File blanks manufactured of superelastic materials generally react in this manner to the conventional twisting methods employed for manufacturing carbon and stainless steel files. Moreover, if superelastic file blanks are over-stressed, such as by being twisted too much during the fluting procedure, the material is subject to failure. For reasons such as these, current manufacturers of endodontic files may resort to grinding the helical profile directly into the superelastic blanks while applying no twisting forces to the blanks. These direct grinding methods are time consuming and expensive. They also limit the variety of cross sectional shapes that may be formed in the final product.
With the above background in mind, it would be desirable to provide a method of manufacturing a wide variety of superelastic endodontic appliances, such as files, using twisting and grinding techniques. In short, it would be advantageous to retain the benefits of superelastic materials and the benefits of a twisting and grinding procedure that simplifies manufacture and allows the production of a wide variety of file cross sections.